Device for distributing a polyphase mixture on a granular solid bed comprising a porous anti-splash nozzle element with flanges

ABSTRACT

A device for distributing a poly-phase mixture in downflow mode over at least one bed of granular solid comprises: 1) at least one tray (P) located above one of said beds of granular solid; 
         2) a plurality of mixer conduits ( 21 ) for producing said poly-phase mixture, each of said conduits comprising at least one upper cross section for flow ( 22 ) that allows the passage of the majority of the gas phase, at least one lower cross section for flow ( 23 ) allowing the mixture formed inside said mixer conduits to communicate with a bed of granular solid, and said conduits being provided over at least a portion of their height with one or more lateral cross sections for flow ( 26 ), allowing passage of the liquid phase inside the mixer conduits, and possibly a minor portion of the gas phase;    3) an assembly of jet breaker type dispersive systems ( 28 ), each dispersive system possibly being associated with each mixer tube or common to a plurality of mixer tubes or even to all of the mixer tubes. Each dispersive system has a controlled porosity and at least a portion thereof is provided with rims ( 100 ), said rims themselves possibly themselves being porous ( 101 ).

The present invention relates to a device for optimising distribution ofa fluid comprising at least one gas phase and at least one liquid phasecrossing at least one bed of granular solid, said phases beingintroduced separately or in a state that is mixed to a greater or lesserextent and said phases being in an overall downflow mode through the bedor beds of granular solid. The invention is applicable to any vessel orreactor comprising, in its upper zone, an inlet for a first liquidfluid, an inlet which may or may not be distinct from the precedinginlet for a second gaseous fluid, and at least one bed of granular solidlocated at a sufficient distance from the upper zone to allowinstallation of a device in accordance with the present invention aswill be described below.

This device can be disposed:

-   -   either at the head of the vessel or reactor, above a first bed        of granular solid;    -   or between two successive granular beds in the case in which        said vessel comprises a plurality of beds of granular solid,        disposed in series along the vessel and separated by a        sufficient distance to allow installation of said device.

The present invention is of particular application in all cases inwhich:

-   -   the gas phase is in the vast majority compared with the liquid        phase, i.e., where the volume ratio between the gas and the        liquid phase is usually more than 3:1 and normally less than        400:1;    -   the reaction is highly exothermic and necessitates introducing a        supplemental fluid, a gas or a liquid, to cool the gas/liquid        mixture. In this case, the fluid is often termed a “quench”        fluid to designate such a supplemental fluid.    -   the reaction requires intimate contact between the phases to        allow a substance, for example hydrogen, to dissolve in the        liquid phase.

In particular, the present invention is applicable to reactions ofhydrocracking, hydrotreatment, hydrodesulphurisation,hydrodenitrogenation and total or selective hydrogenation of C₂ to C₅cuts. It concerns the selective hydrogenation of steam crackinggasoline, the hydrogenation of the aromatic compounds in aliphaticand/or naphthenic cuts, and the hydrogenation of olefins in aromaticcuts. It is also applicable to other reactions requiring good mixing ofa gas phase and a liquid phase, for example partial or completeoxidation reactions, or amination, acetyloxidation, ammoxidation orhalogenation reactions, in particular chlorination.

In the specific field of hydrodesulphurisation, hydrodenitrogenation andhydrocracking, to achieve high efficiency conversions (to obtain aproduct containing, for example less than 30 ppm (parts per million) ofsulphur), as required by the latest gasoline and gas oil specifications,very good distribution of the liquid is necessary as the volume ratiosof gas to liquid are generally between about 3:1 and about 400:1 andusually about 10:1 to about 200:1. When using a quench, very goodcontact is required between the quench fluid, usually a gas, and theprocess fluids. Because of the small proportion of liquid compared withthe gas, one possibility used in the prior art consists, for example, ofusing distributor trays comprising a plurality of apertures for thepassage of liquid and a plurality of downcomers for the passage of gas.Descriptions of such devices can be obtained, for example, from U.S.Pat. No. 3,353,924, U.S. Pat. No. 4,385,033 and U.S. Pat. No. 3,855,068.

However, such solutions cause problems as regards the flexibility of useof the trays, and can also result in irregular supply from the differentorifices if the trays are not perfectly horizontal and/or the because ofthe backflow caused by the huge drop of the liquid and gas streams onthe trays. To overcome such disadvantages, the skilled person has beendirected to use a specific arrangement of a plurality of trays the lastone either being provided with means for collecting and distributing theliquid and gas phases in a separate manner as described, for example, inU.S. Pat. No. 5,232,283, or in the shape of a mixture as described, forexample, in U.S. Pat. No. 4,126,539, U.S. Pat. No. 4,126,540, U.S. Pat.No. 4,836,989 and U.S. Pat. No. 5,462,719. The major disadvantage ofsuch systems is that because of the small quantity of liquid withrespect to the gas, in order to attempt to sprinkle the whole surface ofsaid bed of granular solid properly, the skilled person is led to use ahigh density of downcomers, usually more than 80 downcomers per squaremetre as mentioned in FR-A-2 745 202. The gas velocity in the downcomersis generally from 0.5 to 5 centimetres per second (cm/s) and the liquidvelocity is generally 0.05 to 1 cm/s. These velocities are, however, toolow to allow simultaneous mixing and dispersion.

Because of this absence of liquid dispersion at the outlets from thedowncomers, the skilled person is often constrained to install deflectorplate type systems at the outlet from the orifices or downcomers asdescribed, for example, in French patent FR-A-2 654 952, Internationalpatent application WO-A-97/46303 and in U.S. Pat. No. 5,799,877. All jetbreaker type systems described in the prior art are associated with anaperture and/or a downcomer. They are shaped either as a solid impactplate as described in U.S. Pat. No. 5,799,877, FR-A-2 654 952 and U.S.Pat. No. 4,140,625 downstream of a venture tube, or as a receptacle withvery low walls as described in WO-A-97/46303. The disadvantages of thattype of system arise from the fact that the jet breaker device does notcover the entire surface area of the reactor and that the portion of thegranular solids located below said jet breaker system has very littlechance of being sprinkled with liquid.

The prior art is also illustrated in U.S. Pat. No. 3,524,731 and U.S.Pat. No. 3,431,084 and in U.S. Pat. No. 3,824,080, which describes asystem for mixing a gas phase and a liquid phase having a liquid phasecollector tray, which makes the phases converge towards a central mixingzone in which the liquid phase will collide with the vapour phase. Noneof those patents discloses or suggests a dispersive system that canallow total usage of the bed of granular solid.

The present invention constitutes an improvement to the device fordistributing a poly-phase mixture described in FR-A-2 807 673 which cansupply at least one bed of granular solid with at least one gas phaseand at least one liquid phase, the two phases being in downflow modethrough said bed of granular solid. To clarify the different terms, weshall speak of a distribution device without any other qualification todesignate the distribution device described in FR-A-2 807 673 and weshall speak of an improved distribution device to designate thedistribution device described in FR-A-2 807 673 and comprising theimprovement described in the present application.

More precisely, the invention concerns a device for distributing apoly-phase mixture constituted by at least one gas phase and at leastone liquid phase, said mixture being in downflow mode through at leastone bed of granular solid, said device comprising:

-   -   at least one tray (P) located above one of said beds of granular        solid;    -   a plurality of mixer conduits (21) for said liquid and gas        phases, each of said conduits comprising at least one upper        cross section for flow (22) allowing the passage of the majority        of the gas phase, and at least one lower cross section for flow        (23) allowing the mixture formed inside said mixer conduits to        communicate with a bed of granular solid, said mixer conduits        (21) being provided with one or more lateral cross sections for        flow (26) over at least a portion of their height to allow the        passage of the liquid phase and possibly a minor portion of the        gas phase inside the mixer conduits;    -   a jet breaker type dispersive system (28) having a controlled        porosity disposed below the lower cross section for flow (23)        and above the bed of granular solids, said distribution device        being characterized in that at least a portion of a perimeter of        the dispersive system is provided with rims (100) or (101).

The invention will be better understood from the accompanying figures inwhich:

FIG. 1 shows an axial cross section through a device of the invention;

FIG. 2 shows a view of an assembly of a distributor plate associatedwith mixing tubes and a porous dispersive element;

FIGS. 3 and 4 show diagrams of porous dispersive systems provided withrims associated with one or more mixing tubes perforated with slots ororifices;

FIGS. 5, 6 and 7 show low and high liquid quantity zones in accordancewith the prior art and with the invention.

The bed or beds of granular solid are contained in a reaction vesselhereinafter termed a reactor, which in general comprises, in thedirection of flow of the phases, a system for introducing phases (notshown in FIG. 1), a device (11) acting to pre-mix said phases, animproved distribution device for the poly-phase mixture, supported by atray (P), and comprising elements (21), (28) and (100) or (101) locatedin the upper portion of said vessel (E) or between two beds of granularsolid (13) and (14) of said vessel. The improved distribution device cansupply one or more beds of granular solid (13) and (14). When thereaction vessel comprises a plurality of granular beds disposed inseries along said vessel, each can be fed by an improved distributiondevice. In the most general case, between two consecutive granular bedsand upstream of the improve distribution device, the vessel can comprisea system for introducing a supplemental gas or liquid (16) and a system(15) for mixing said supplemental fluid with the gas and liquid phasesfrom the immediately superior bed (13). A mixing system (15), usuallytermed a “quench box” in the context of the invention shapes the subjectmatter of other patents, in particular the Applicant's French patentapplication FR-01/06213 in its most developed shape. Said mixing system(15) is entirely compatible with the device described in the presentapplication. The improved distribution device of the presentapplication, in which FIG. 2 shows a diagram without showing the rims,comprises in its most general shape:

-   -   1) at least one tray (P) located above one of said-beds of        granular solid;    -   2) a plurality of mixer conduits (21) which are substantially        cylindrical in shape and orientated with a substantially        vertical axis, supplied with said liquid and gas phases,        allowing them to mix. Each of said conduits comprises at least        one upper cross section for flow (22), and at least one lower        cross section for flow (23) allowing the mixture formed inside        said mixer conduits to communicate with a bed of granular solid,        said mixer conduits being provided with one or more lateral        cross sections for flow over at least a portion of their height.        Said upper cross section for flow (22) allows the majority of        the gas phase to pass and said lateral cross section for flow        (26) allows the passage of the liquid phase inside the mixer        conduits possibly along with a minor portion of the gas phase;    -   3) at least one jet breaker type dispersive system (28) disposed        below the lower cross section for flow (23) and above the bed of        granular solids, said system possibly being associated with each        mixer conduit as shown in FIG. 4, being common to a plurality of        mixer conduits as shown in FIG. 3, or being common to all of the        mixer conduits on a tray (P) as shown in FIG. 2. Each dispersive        system has a substantially flat horizontal geometry, but may        have a perimeter of any shape. It has a controlled porosity and        it may be provided over at least a portion of its perimeter with        rims (100) (FIG. 3) of any shape, said rims possibly themselves        having a porosity (FIG. 3).

The dispersive system can be suspended on tray P or the lower end of themixer conduits.

The mixer conduits, which are substantially cylindrical in shape andwith a practically constant cross section, have diameters in the range0.3 to 10 cm, preferably in the range 1 to 5 cm. Their height can be inthe range 100 to 500 millimetres, preferably in the range 250 to 400millimetres. The number of mixer conduits per unit cross section of trayis in the range 1 to 80 conduits per square metre, preferably in therange 5 to 50 conduits per square metre. In certain cases, it may beadvantageous to provide liquid phase drainage orifices at the level ofthe tray (P). The cross section for flow of this set of orifices is suchthat the fraction of the liquid phase flow passing via said drainageorifices is less than 10% of the total flow of the liquid phase inmovement and preferably less than 5% of the total flow.

It should be noted that in FIGS. 3 and 4, the mixer tubes are allintegral with the tray (P) and extend below the tray (P) by a distance(z) corresponding to the zone denoted (25) in FIG. 4, the value of saiddistance (z) being less than or equal to the distance (d) separating thelower end of a mixer tube (23) from the dispersive system (28) withwhich it is associated. Distance (d) is generally in the range 5 mm to500 mm.

Further, the distance (D) separating the jet breaker type dispersivesystem from the bed of granular solids located immediately below it isselected to conserve the mix of the gas and liquid phases as close aspossible to that at the outlet from the mixer tube. In practice, saiddistance (D) is in the range 0 to 500 mm. The upper portions of themixer tubes are surmounted by caps (24) intended to disturb jetsderiving either from the inlet conduit for liquid entering the reactor(not shown in the Figures) or from the upper bed of granular solids,i.e. located immediately above the distribution device underconsideration, and to separate the gas and the liquid. These caps (24)can have any shape, as is well known to the skilled person.

Ingress of each of the gas and liquid phases into the mixing tubes canbe made in a separate manner as far as possible, the gas phase enteringvia the upper cross sections (22) protected from the ingress of liquidby caps (24) and the liquid phase entering via the lateral crosssections (26) possibly with a small fraction of the gas phase.

Said mixer conduits (21) are provided with lateral cross sections forflow (26) which are orifices (FIG. 3) or slots (30, FIG. 4) of any shapepierced at the periphery of the mixer tubes over one or more levels,preferably over at least three levels. It is important to have a minimumdistance (h) between the upper face of the tray (P) which receives theliquid and the orifices located on the level closest to said upper faceor, in the case of slots, between the bottom of each slot and the upperface of the tray (P). This height (h) is often in the range 5 to 250millimetres, preferably in the range 50 to 100 millimetres. Further, theorifices or slots are pierced on the periphery of the mixer tubes toform, in the thickness of the wall of said mixer tubes, an angle alphawith respect to the horizontal the value of which can very between 0 and60° and preferably between 0 and 45°. This angle is advantageouslydirected downwardly to encourage contact between the liquid phaseentering via the orifices (26) and the gas phase entering via the uppersections (22), by imposing a vertical downflow component on said gasphase.

Ingress of the phases into the reaction vessel can occur separately oralready in a pre-mixed state. More precisely, the upper portion of thereaction vessel (E) shown in FIG. 1 can comprise a pre-distributor (11)upstream of the bed of granular solid (13), which can carry out aninitial imperfect mixing of the gas and liquid phases. Pre-mixing of thegas and liquid phases distributed by the device (11) occurs in adownflow manner to the first distribution tray (P).

It should also be noted that the jet breaker type system can, ifappropriate, be associated with each mixer tube (FIG. 4) individually,associated with a plurality of mixer tubes (FIG. 3) or with the assemblyof mixer tubes contained on a tray (P). Further, said dispersive systemscan be placed on a plurality of levels as shown in FIG. 4.

French patent FR-A-2 807 673 describes that the porosity of the jetdistributor type system, defined as the ratio of the void surface to thetotal surface area, is in a ratio of 2% to 80%, preferably about 5% to50% and usually about 5% to about 30%. The porosity range for adispersive system in accordance with the invention is identical to thatin French application FR-A-2 807 673 and is selected as a function ofthe surface speeds of the gas and liquid phases, the densities and theviscosities of each phase, and of the surface tension in relation to thenature of the surface of the dispersive system.

When the dispersive systems are not necessarily in the same horizontalplanes, the projection over the cross section of the reactor of thedispersive systems belonging to different planes is such thatoverlapping substantially does not occur and it covers substantially theentire cross section of the reactor. The distance separating twodifferent planes is generally in the range 1 to 250 mm, preferably inthe range 5 to 180 mm and more particularly in the range 10 to 80 mm.This disposition of the dispersive systems over a plurality of planesallows a better flow of gas and better homogenization thereof over theentire cross section of the reactor. In the case of a fluctuating flowin the gas phase, this staggering can also allow smooth evacuation ofany momentary excess of said gas.

The dispersive systems can have any geometric shape, but are usuallysubstantially circular, rectangular or triangular in shape. They arepreferably located in horizontal planes, or as close as possible to thehorizontal plane, as this condition is difficult to produce inindustrial vessels the diameter of which can be 5 metres or more. Theproposed improvement means that the tolerance on said horizontalcriterion is eased, as will be described below in more detail.

The advantages of the improved distribution device over the prior artcan be summarized as follows:

-   -   a) the relatively low density of the mixer conduits, preferably        5 to 50 conduits per square metre, and their diameter,        preferably in the range 1 cm to 5 cm, allows an increase in the        speed of the gas and liquid phases inside the mixer conduit and        thus encourages contact and good mixing of the phases.    -   b) The dispersive system covering almost the entire cross        section of the reactor allows this mixture to be distributed        over the entire cross section including, because of the porosity        of the dispersive system, over the zones of said cross section        corresponding to the projection of the dispersive system which        would not be irrigated in the absence of said porosity.    -   c) Since the filing date of French patent application FR-A-2 807        673, it has been discovered that the addition of rims to at        least a portion of the dispersive systems ensures more        homogeneous distribution of the mixture of the gas and liquid        phases deriving from the mixing conduits. These rims retain a        certain amount of the gas and liquid mixture and guarantee that        the whole porosity of the dispersive system will be well fed.        This is particularly advantageous with large industrial units        the diameter of which can be 5 metres or more, in which it is        always difficult to guarantee that the trays (P) and thus the        associated dispersive systems will be completely horizontal.        Without such rims, the gas and liquid mixture arriving at the        dispersive system could flow preferentially over a certain        portion of said system, leaving another portion without        irrigation.

The rims can be 0.2 to 1 time the diameter of the conduits, for examplebetween 2 and 50 mm. They can themselves have a porosity in the range 0to 80%. They may or may not be inclined to the vertical, and theirinclination will generally be in the range −40° to +60° and preferablyin the range −30° to +45°, these angles being with respect to thevertical, with positive values corresponding to rims inclined outwardlyof the dispersive system, and negative values corresponding to rimsinclined inwardly of the dispersive system. Clearly, when the dispersivesystems are on different horizontal planes and have rims, the distanceseparating said horizontal planes must be greater than the height of therims.

The rims could concern only a portion of the dispersive systems, theother portion not having said rims. It will often be preferable to equipthe dispersive systems located on planes closest to the bed of granularsolid with rims. In certain cases, it may also be advantageous for agiven dispersive system to have rims over only a portion of itsperimeter. The precise geometrical shape of said rims could vary; inparticular, the upper end of the rims could be curved inwardly. Near therim of a dispersive system, the porosity of the dispersive system isadvantageously zero. The term “near the rim of a dispersive system”means the zone located at a distance of 30 mm or less from the rim,preferably 10 mm or less from the rim.

One function of said rims and their zero porosity environs is to retaincertain impurities that may be contained in the liquid feed,particularly when it is constituted by heavy hydrocarbons such as cutswith a boiling point of more than 350° C., as is the case in heavy gasoil type hydrotreatment units.

In this case, the zone near the rims progressively becomes charged withthose impurities, and contamination of the bed of granular solid is thusprevented.

The comparative example below will provide an appreciation of theadvantages of the presence of rims. The measurements taken weremeasurements of the liquid distribution in a cross section of a reactorwith a 600 mm diameter. They were made using a gamma ray tomograph whichallowed zones carrying a lot of liquid to be observed in black on thefigures, and zones with a small amount of liquid to be observed in whiteor grey in FIGS. 5, 6 and 7 (viewed from below).

The following three systems were compared:

-   -   1) a prior art distribution system comprising 7 mixer tubes with        an internal diameter of 50 mm and 300 mm in height, but without        a dispersive system;    -   2) a distribution system in accordance with FR-A-2 807 673,        comprising 7 mixing tubes associated with 3 porous jet breaker        type dispersive systems having a porosity in the range 10% to        40% and disposed in the same substantially horizontal plane. The        diameter of each dispersive system was about one third of the        diameter of the vessel;    -   3) an improved distribution system comprising 7 mixer conduits        identical to those in the preceding case, associated with 3        porous jet breaker type dispersive systems having a porosity in        the range 10% to 40%, and provided with non porous rims 20 mm in        height, and substantially vertical, in accordance with the        invention.

The liquid phase was constituted by a mainly C7 hydrocarbon cut and thegas phase was constituted by nitrogen. The ratio of the gas to theliquid flow rates was in the range 20 to 100 by volume.

In FIG. 5 (corresponding to the prior art distribution system), it canclearly be seen that the liquid distribution is poor: the trace of the 7tubes is visible, which indicates the presence of a great deal of liquiddirectly below the outlets from said mixing tubes. In FIG. 6(corresponding to the distribution system of French patent applicationFR-A-2 807 673), the liquid is distributed better since the trace of themixing conduits can no longer be distinguished. In contrast, a slightoverflow of liquid is noted in the three dispersive systems the trace ofwhich is still visible. In FIG. 7, corresponding to the presentinvention, the trace of the three dispersive systems has completelydisappeared, which indicates that the liquid is homogeneouslydistributed over the whole cross section of the reactor. Thisdistribution was retained over the tested range of volume ratios for thegas and liquid flows.

1. A device for distributing a poly-phase mixture constituted by atleast one gas phase and at least one liquid phase, said mixture being indownflow mode through at least one bed of granular solid, said devicecomprising: at least one tray (P) located above one of said beds ofgranular solid; a plurality of mixer conduits (21) for said liquid andgas phases, each of said conduits comprising at least one upper crosssection for flow (22) allowing the passage of the majority of the gasphase, and at least one lower cross section for flow (23) allowing themixture formed inside said mixer conduits to communicate with a bed ofgranular solid, said mixer conduits (21) being provided with one or morelateral cross sections for flow (26) over at least a portion of theirheight to allow the passage of the liquid phase and possibly a minorportion of the gas phase inside the mixer conduits; a jet breaker typedispersive system (28) having a controlled porosity disposed below thelower cross section for flow (23) and above the bed of granular solids,said distribution device being characterized in that at least a portionof the perimeter of the dispersive system is provided with rims (100) or(101).
 2. A device according to claim 1, in which the jet breaker typedispersive system has a porosity of about 2% to about 80%, preferably inthe range 5% to 50%, and more preferably in the range 5% to 30%.
 3. Adevice according to claim 1, in which a jet breaker type dispersivesystem is associated with each mixer conduit.
 4. A device according toclaim 1, in which a jet breaker type dispersive system is associatedwith a plurality of mixer conduits that are close to each other.
 5. Adevice according to claim 1, in which a jet breaker type dispersivesystem is associated with all of the mixer conduits of the distributiondevice.
 6. A device according to claim 1, in which the lower end of themixer conduits is located at a distance (d) of about 5 to 500millimetres from the jet breaker type dispersive system.
 7. A deviceaccording to claim 1, in which the jet breaker type dispersive system islocated at a distance (D) from the bed of granular solid, which isselected to substantially conserve the quality of the mixture formedinside the mixer conduits (21) and leaving said mixer conduits via thelower cross sections for flow (23) until it is distributed over thedownstream granular bed.
 8. A device according to claim 1, in which thedensity of the mixer conduits is 1 to 80 conduits per square metre,preferably 5 to 50 conduits per square metre.
 9. A device according toclaim 1, in which the cross section of the mixer conduits issubstantially constant.
 10. A device according to claim 1, in which theheight of the mixer conduits is in the range 100 to 500 millimetres,preferably in the range 250 to 400 millimetres.
 11. A device accordingto claim 1, in which the angle of the rims with respect to the verticalis in the range −40° to +60°, the negative sign corresponding to rimsinclined inwardly of the dispersive system and the positive signcorresponding to rims orientated outwardly of the dispersive system. 12.A device according to claim 1, in which the porosity of the dispersivesystem is zero near to the rims, “near” corresponding to a distance fromthe rim in the range 30 to 0 millimetres, preferably in the range 20 to0 millimetres.
 13. A device according to claim 1, in which the height ofthe rims of one or more jet breaker type dispersive systems is 0.2 to 1time the diameter of the mixer conduits and advantageously in the range2 to 50 millimetres, with a porosity in the range 0 to 80%.
 14. A deviceaccording to claim 1, in which the dispersive systems are staggered overat least two levels, said levels being spaced apart by a height in therange 1 to 250 millimetres, preferably in the range 5 to 180 millimetresand more preferably in the range 10 to 80 millimetres.
 15. A deviceaccording to claim 1, in which the orifices or lateral slots (26) of themixer conduits (21) are cut to have, in the thickness of the mixerconduits, an angle alpha with respect to the horizontal the value ofwhich is in the range 0° to 60°, preferably in the range 0° to 40°. 16.A device according to claim 1, in which the dispersive systems aredisposed over a plurality of planes and in which the dispersive systemslocated on planes closest to the bed of granular solid comprise saidrims.
 17. Application of a device according to claim 1 to distributing apoly-phase mixture at least part of the gas phase of which isconstituted by hydrogen